1. Field of the Invention
This invention relates to modifying the surface of particles for improved dispersion characteristics in aqueous, solvent, resinous, polymeric, cementitious, magnetic or the like application systems. In particular, this invention relates to a pigment or filler particle whose surface is coated with at least one electric charge modifying agent which may also be combined with at least one dispersion promoting agent, which has improved dispersibility, coloring, handling, and other processing properties in application systems. Even more particularly, this invention relates to an iron oxide pigment particle whose surface is coated with at least one inorganic electric charge modifying material and at least one dispersion promoting material.
2. Prior Art
Inorganic pigments such as metal oxides, for example, iron oxides, are conventionally used as coloring components in the construction, paint, plastic and other industries. The inorganic pigments are incorporated for coloring into the desired application system such as, aqueous, solvent, resinous, polymeric, cementitious or dispersion systems or the like usually through intensive mixing. A key performance property of the pigment is the dispersibility of the pigment throughout the application system. The dispersibility is a measure of the ease with which the pigment particles can be uniformly and intimately mixed in the application system. Poor dispersion of the pigment particles can cause large agglomerates of pigment particles which may result in surface imperfections, color streaks, non uniform coloration or incomplete color development within the end product.
A problem with many inorganic pigments, for example, metal oxides, is that they normally do not disperse well in mediums such as in paints, plastics, cements or the like. A reason for this is that the surface of metal oxide pigments is not electrochemically compatible with many application systems and as a result, additional time, greater mechanical energy, and greater pigment quantities are required to properly mix the pigment in the medium to achieve the desired color and other properties.
Attempts have been made to provide a pigment particle with enhanced dispersion and coloring properties for many application systems. Among the prior art, surface modifications of inorganic pigment particles by coating the particles with inorganic additives are known for improving coloring and processing properties in several application systems. European Patent No. 87113450.8 - Burow et al. and U.S. Pat. No. 5,059,250 - Burow et al. disclose coating iron oxide pigment particles with colorless inorganic additives selected from the group of Mg, Zn, Al, La, Y, Zr, Sn and Ca. The isoelectric point of the coated particles is thereby adjusted by the coating to be greater than 7 which Burow et al. claim improves the coloring properties of the pigment in many application systems.
U.S. Pat. No. 4,053,325 - Vanderheiden discloses a iron oxide particle coated with an insoluble metal metaphosphate of the formula M(PO.sub.3).sub.x , where M is a metal selected from the group of Al, Ba, Ca, Mg, Fe and Zn, this coated particle is claimed to improve the thermal stability of the pigment in many application systems.
It is also known, to treat inorganic particles with specific organic materials to improve certain performance characteristics in many application systems. U.S. Pat. No. 4,753,679 - Damtano et al. disclose a method for improving the strength and water permeability of concrete using inorganic particles, such as iron oxide, which have been pretreated with a fatty acid, such as stearic acid or oleic acid, to promote the dispersal of the particles in concrete systems.
U.S. Pat. No. 4,952,617 - Ayala et al. disclose surface modified inorganic pigment particles coated with an organic surfactant for improved dispersibilty and heat stability in both water based and organic solvent coating systems.
U.S. Pat. No. 4,946,505 - Jungk discloses a method of dyeing concrete using a specific binder physically combined with pigment particles, such as iron oxide, into a granule bead. However, these modified pigment particles suffer from the shortcoming that the dispersal of the pigments is dependent on the dissolution of the granule beads, or in other words, the dissolution of the pigment particles from the binder. Hence, the dissolution may occur prior to the pigment being dispersed in the concrete systems. The level of attachment of the pigment particle to the binder is, therefore weak, the pigment being only physically combined or encapsulated within the binder.
Despite the many prior attempts at improving pigment particle performance in a variety of application systems, more effective means are constantly being sought. It would be desirable to provide particles, namely pigment or filler particles, which have been surface modified to improve the particle performance in all application systems. It would also be desirable to be able to electrochemically and chemically modify, adjust or control a particle surface to provide a particle which has improved processing properties, such as dispersibility. It would also be desirable to specifically design the surface modification on the particle to be compatible with any desired application systems. It would also be desirable to provide a generic method for surface modification that is applicable to all particles and compatible with all application systems.